The present invention relates to a valve actuation (VA) apparatus for an internal combustion engine, and more particularly, to an improvement in positioning of a crank arm.
Typically, a VA apparatus for an internal combustion engine, adapted to the engine having two intake valves per cylinder, comprises a driving shaft that rotates in synchronism with a crankshaft, a crank cam arranged at the outer periphery of the driving shaft and having an axis eccentric with an axis of the driving shaft, and two cylindrical camshafts coaxially rotatably arranged at the outer periphery of the driving shaft.
The camshafts have a pair of valve operating (VO) cams integrated with the outer periphery to correspond to a pair of intake valves. Torque of the crank cam is transmitted to the VO cams through a transmission mechanism or multi-node linkage, opening/closing the intake valves through valve lifters.
The transmission mechanism comprises a rocker arm arranged above the VO cams and swingably supported on a control shaft through a control cam, a crank arm having at one end a circular portion rotatably linked to the crank cam and at another end a protrusion rotatably coupled to a first arm of the rocker arm between two forked portions through a pin, and a pair of link rods each having a first end rotatably coupled to a corresponding one of two bifurcated portions of a second arm of the rocker arm through a pin and a second end rotatably coupled to a cam nose of the VO cam.
The VO cams are arranged symmetric with respect to the crank cam (crank arm), and are swung at the same time by the bifurcated second arm to prevent occurrence of variations in opening/closing lift of the intake valves.